Apparatus for liquefying and separating gas mixtures



R. MEWES APPARATUS FOR LIQUEFYING AND SBPARATING GAS MIXTURES Filed March 30. 192' INVENTOR A TTORNE Y Patented Oct. 7, 1924.

AEPARATUS FOB LIQUEF 5 ii Application filed arch 80, 1921. Ber-Isl no. reactors To all whom it may concern:

'Be it known that I, RUDOLF Mnwns, a citizen of Germany, residing at Berlin, Germany, have invented certam new and useful 5 1m rovements in Appgratus for L1queyin an Separating Gas ixtures (for which have obtainedLettersPatent in Germany, No. 317,889, on an application filed April 28, 191%),01? which thejfollowing is a specification.

This invention relates to an improved apparatus for li uefying and separating gas mixtures, the o ject of the invention emg to provide an apparatus by means of which the separation of the gases is accomplished. by rectification or fractional distillation at a temperature considerably higher and at correspondingly higher pressure and' smaller volume than was heretofore deemed possible.

A further object of the invention is to provide an apparatus by means of which the P complete separation of the gases can be accomplished 1n a single operation, and which apparatus is extremely economical in operation.

A further object of the invention is to rovide an apparatus by means of whic a cooling element is conducted downwardly through the gases to be separated, the cooling element bein maintained out of direct contact with sai gases, the present invention being an im rovement in part upon that described and c aimed in Letters Patent of the United" States No. 1,888,191, issued to me June 20, 1916.

The known processes for rectifying gas mixtures such as air, water-gas or the like are based on the assumption that a temperature which is at least as low as 191 Celsius is required at the coldest part of the oxygen separating apparatus so that the drop of temperature available for the process of rectification amounts to the difierence between -182 and 191 Celsius, or -182 which is in the most favorable condition, between -182 and -196. In other words, the drop of temperature varies between a minimum of 9 and a maximum of 1?. According to the prior state of the science rectification and 193, or, when carried on in a vacuum,-

and technics of gas distillation it did not ap pear possible to exceed these limits in t e ractice of extracting oxygen and nitrogen rom the air.

Butin rectifying at these temperatures no matter whether it is a question of 'recti cation in a narrower sense or of a multi-e rocess or de hlegmation, t e appreclable isadvantage as to be coped. with that the volumes to be dealt with would be very large at the pressure of the atmosphere and at slightly lower pressures, and hence the losses of cold. by thermal leakage throu h the walls or the separating vessel woul also be relatively large amounting to 05 as much as 20 to 25%.

Besides, the apparatus required is very large and expensive; a fact which renders the rocess 0 separation uneconomical, partic tis arly m the cases of plants for small out- A circumstance that is very unfavorable for the thermo-dynainic efliciency of the said process is that it is necessary to employ temperatures as low and lower than 191, this, as is well known, being a great drawback. in constant working, because it involves great leakage through the metallic walls.

For the purpose of describing the prin; cipal features of the invention it will be asso sumed that oxygen and nitrogen are to be extracted from atmospheric air and that the lowest temperature in the interior of the separating or distilling column shall not go below 170 Celsius. This temperature 35 corresponds. to a pressure of the nitrogen vapor in the column amounting to about 15 atmospheres, instead of 5 atmospheres as in the old process. 'llhe boiling point of oxygen at a pressure of 15 atmospheres lies at about 110 Celsius. In this way a useful or efiective dro of temperature of about elsius is obtained. But the efi'ect is enhanced by the nitrogen, which boils at a temperature of 170 under a 95 pressure of 15 atmospheres, being allowed to expand in a cooling coil until its pr dro s to 1 atmosphere. This results in the int of the nitrogen sinking to boi mg po -196, so that the total drop of tegm me ture amounts to 19614e0=56. With the old process as he before stated, the greatest drop of temperature obtainable in the column in spite of the increase of pressure would be approximately 15i-Celsius, because not pure oxygen, but a m xture of per centof oxygen and whose boiling is -l is obtained.

An additional factor is that by the abovementioned increase of temperature from l9l to llZ0 a technical efiect is obtained which, accordi to scientific measents me by Bailey, results in the nitrogen vapor takin up much less oxygen mr unit of weight w en saturated than at the lower n -r atures and pressures of the old Vfith the invention it is'possi'ble to decrease the saturability by oxygen of the nitrogen vapor under pressure at will by partly cooling down the nitrogen vapor to a temperature considerably under its boil ing point, this being done by cooling elements past which the vapor flows and which are located at some distance from the point in the column where the said vapor is conducted out. B this means the last traces of oxygen in t e vapor are condensed and separated from the nitrogen. --lln other words, the recess for low temperatures and pressures escribed in the German Patent 227,100 is adapted to higher pressures and temperatures and used in the present invention for removing the last traces of oxygen from nitrogen vapor, or for sifting it out as it were and conducting it away further back in the separating device.

An important feature in the present invention is that the medium in the column is not cooled-by mixin the cold nitrogen with this medium but y contact with the surface of a conduit through which the cold nitrou is conducted, this conduit taking the of an evaporatin coil orcoils. Further features are the utllization of the cold of the liquid oxygen, the shifting of the interval between a higher and a lower temperature' to a difi'erent part of the temperature scale and in reducing at the same time the proportion of oxygen in the nitrogen vapor and in decreasing the gas volume whilst maintaining the wei ht per unit of space or making it larger t an it could be made hitherto.

The scientific foundation underlying the present invention, consists in the fact discovered by me that no matter what pressure is applied to aseous nitrogen it will never absorb more t an the same definite amount of saturated oxygen at the same tempera- 'ture. From analogies regarding the saturation of air with steam at difierent pressures and from the law of partial volumes I have found that the same laws hold for mixtures of nitrogen and oxygen vapor as for steam.

An impot advan of the present invention consists in the. act that it is not necess r v to liquefy the whole of the air to be dist 1 ed but only a certain fraction of the same sothat the oxygen can, as it new. siftw or washed out at a higher pressure thanthat of the atmosphere. The condensed liquid and the cooling vapors, contrary to modes of operation employed hitherto, flow in one and the same direction, the stream of cooling vapors being subdivided or made to flow through a plurality of pasta or pipes. The unidirectional flow of the condensed liquid and the coolinghvapors is dueto the fact that the vapor w ich condenses in the top of the distilling chamber or in any part of this chamber iquefies by contact with the cooling elements chilled b the expanded cold vapors and then flows own on the exterior surfaces of these elements in the same direction as the cooling vapors in them on account of its greater specific gravity.

In accordance with the present invention the cooling operation is due to conduction, or the transmission of cold through the cooling walls of the cooling elements. Besides, only one pressure stage is used in the distilling column. The liquid nitrogen formed in the cooling pipe is not conducted into the interior of the column but through a pipe or passage passing through the column. By this arrangement the cold of evaporation only is made available in the interior chamber of the column but the refrigerant itself is not introduced into the said chamber but immediately conducted away in a vaporous state] By this means the important technical advantage is obtained that the oxygen and the nitrogen can be separated from each other in one operation by the regenerative process under any pressure in the separating chamber, no matter what kind of process is employed for the actual separation of the gases. The pressure may be increased up to the critical pressure of nitrogen or oxygen without detriment to the process. The process maybe carried out with low pressures.

A separating or distilling column for carrying out the process is diagrammatically illustrated in the drawing. The condensed liquid and the cooling vapors both travel downward from the top part of the column, the cooling vapors being conducted downward by the coils b and 0 while the condensed liquid in the interior of the column trickles down on the surfaces of the coils b and 0. The coils b and 0 may each be subdivided into a number of collateral branch pipes. it is obvious that the con densed liquid that is formed on the surfaces of the cooling elements or pipes b and c of the column, or in fact in any part of the distilling column, flows downward on achere ' throug the oxygen or pure nitrogen ofany air liquefying count of its higher specific gravity, i.'e. it travels in theme directionas the refri erant vapors in the cooling pipes -b an 0. The separation of the oxygen and nitrogen is accomplished in the distilling column in one operation in thefollowin manner:

The li uid nitrogen forme in the cooling coil b is not introduced into the interior. of the column but, after having assed down through the valve is, is allow to expand ina s ecial cooling pipe 6 which passes the column. y this arran ment the cold of evaporation only of t e exanded nitrogen is made available in the interior of the chamber a, but the refri rant itself or the carrier of the said col is not introduced into the chamber but is immediately conducted away in a 'vaporous state. By this means the advantage is obtained that the oxygen and nitrogen may be completely separated by the regenerative process in a single operation at any pressure in the separating chamber, no matter whatparticular process is used, for the actual separating operation. The pressure may be raised u ito the critical ressure of t e nitrogen wi out detriment to the rocess.

The li ui oxygen is conducted awai from the ttom d of the column a: throng the pipe 12. and the valve 5 to the oxygen evaporator or cooling chamber 6, from whence it flows in a vaporous state through the pipe 0, which merges into a cooling coil in t e upper part of the column as shown.

The liquid air formed in the liquefying coil f is conducted through the pipe f into the interior of the column a, while the cold of the gases conducted away through prolongations of the pipes b and 0 may be turned to account in a known-manner in a heat exchanger (not shown).

In the co umn a under pressure, pure liquid oxygen is obtained at the bottom d and in its upper part is (produced, the heat of w ose vapor is carrie ofi by pipe b and thus made available for use in a counter current heat exchanger after it has left the separatin column.

he novel method of operation permits process being used conjunction with t This can be done b inserting an expansion valve 9 (throttle evice) or an expansion machine in the inflow conduit car ing ire compressed air into the bottom 'queig'ing coil and thus producing by expansion 0 the compressed a1r until 1ts pressure sinks to that existing in the liquefying coil, the cold necessary to make up for the losses due to radiation etc., and for the continuous operation of the plant. The cold vapors or gases passing out of the separator a deliver up their cold in the counter current heat exwhose interior space is end of-t e column -forming secondary coil with the upperpart of said coolin chamber in. and having its e separating column.

changer to the fresh compressed medium in the well known manner. a

To enhance the thermo-dynamic efliciency of the process in cases in which an expans1on machine is emplloyed, the vaporous ni trogen may be re eated in any suitable manner. 4 v

I claim:

1. An apparatusof the class described, comprising, in combination, a rectifyin column, means for introducing compresse gas into said column, a cooling chamber disposed above said column, a gas conduit in communication with the u per end of said column "and passing throug relieving device in communication with said conduit, and a cooling conduit .in the upper end of the column, said cooling conduit communicating at one end with said tension-recommunication with the upper end of said column and merging into a coil within said chamber, a tension-relieving device in communication with said coil, and a cooling coil in the upper end of the column, said coil forming a passage communicating at one end with said tension-relieving device and having its delivery end outside of said column. v

3. An apparatus of the class described, comprising, 1n combination, a rectifying column, means for introducing compressed gas into said column, a coolin chamber above said column, a gas conduit 1n communication with the upper end of said column and merging into a coil within saidchamber, a tension-relieving device in communication with said coil a primary cooling coil in the upper a passage comsaid tension-reits delivery and a secondary coolsaid municating at one and wit lieving device and havin outside of said column, an ing coil in the upper part of the column,

communicating at one en delivery end outsi e of said column.

4. An comprising, m combination, a rectifyi column, means for introducing compresse gas into said column, a cooling chamber above said column, a gas conduit in communication with the upper end of said column and merging into a coil within said chamber, a tenslon-relieving device in communication with said coil, a primary cooling coil in the upper end of the column and communicating at one end. with said' tension-relic device and having its delivery end outsi e of said chamber, a tension eoolmg ap aratus of the class described,

4i, emme I said column, a secondary cooling coil in the In testimony whereof I have signed this upper part of the column and commufnicntspecification in the presence of two Witw ing at one end with the upper part of saidl nesses.

cooling chamber and havin its deliverye'ndl 3 a conduit com- RUDOLF MEWES.

outside of said column, an municating at one end with the lower enol Witnesses: of the column and at the other end with the REITHE SEECK,

upper part of the cooling chamber. ()TTo SCHNEIDER. 

